Air conditioning systems are currently commonplace in homes, office buildings and a variety of vehicles including, for example, automobiles. Over time, the refrigerant included in these systems becomes depleted and/or contaminated. As such, in order to maintain the overall efficiency and efficacy of an air conditioning system, the refrigerant included therein is periodically replaced or recharged.
Portable carts, also known as recover, recycle, recharge (“RRR”) refrigerant service carts or air conditioning service (“ACS”) units, are used in connection with servicing refrigeration circuits, such as the air conditioning unit of a vehicle. The portable machines include hoses coupled to the refrigeration circuit to be serviced. A vacuum pump and compressor operate to recover refrigerant from the vehicle's air conditioning unit, flush the refrigerant, and subsequently recharge the system from a supply of either recovered refrigerant and/or new refrigerant from a refrigerant tank.
Refrigerant vapor entering the ACS unit is first passed through a filter and dryer unit to remove contaminants and moisture from the recovered charge and then through an accumulator to remove oil entrained in the refrigerant from the air conditioning system. The refrigerant is then pressurized by a compressor before it is stored in a storage tank.
In typical ACS units, the pressure of the refrigerant flowing into the accumulator is regulated by an expansion valve upstream of the accumulator. The expansion reduces the pressure of the incoming refrigerant, which serves to change the state of the refrigerant from a liquid to a gas. Since the oil boils at a lower pressure than the refrigerant at a given temperature, the oil remains in a liquid state and is separated from the vaporized refrigerant. The refrigerant exiting the accumulator must be in the vapor state to prevent liquid refrigerant from entering the compressor, which can cause damage to the compressor. The expansion valve typically sets the pressure in the accumulator as a constant value, which is near the saturated vapor pressure of the refrigerant at the coldest ambient temperature at which the unit is allowed to be operated. For example, in a typical ACS unit, the accumulator is pressurized to 35 psi, which is slightly below the saturated vapor pressure of R134a at 50° F.
Operating the accumulator in an ACS unit at a higher pressure reduces recovery time, increases recovery efficiency, and improves oil separation performance. What is needed, therefore, is an ACS unit which operates at varying operating accumulator pressures in order to optimize recovery performance.